I. Field of the Invention
This invention relates generally to automatic or semi-automatic firearms and more particularly to a breech block locking mechanism for maintaining the bolt in rigid locked relationship with respect to the shell chamber during firing and for subsequently releasing the bolt for rearward motion during extraction and ejection of the spent cartridge.
II. Description of the Prior Art
Various arrangements are knwon in the art for withdrawing a cartridge from a magazine, urging the cartridge into the chamber and for locking the bolt behind the chamber during firing and for subsequently automatically unlocking and moving the bolt in a rearward direction to extract the spent cartridge casing from the chamber and eject it from the firearm. For example, in the Amsler U.S. Pat. No. 2,890,626 there is described a firearm having a bolt which is slidably movable in a breech body and which includes a locking arrangement having two cylindrical rods cooperating with curved faces formed in two locking grooves. While the pins function to lock the bolt relative to the breech block during the firing segment of the operating cycle, the device of the Amsler Patent must rely upon a number of springs and pawls for accomplishing the locking function. As such, the firing mechanism is subject to undue wear and necessary maintenance and replacement.
The Stecke U.S. Pat. No. 2,089,671 describes a breech block locking arrangement in which two symmetrical locking levers are carried by the breech block and mounted therein so as to be rotatable and slidable relative to the breech block. These locking levers have outer arms which cooperate with inclined walls such that during a short initial rearward movement of the breech block, the locking levers are turned by the inclined walls to impart a relatively slow initial movement rearward, followed by a more rapid translation of the breech block or bolt member following this initial period.
The present invention relates indirectly to each of the aforementioned prior art patents but is deemed to be a substantial improvement over the devices described therein. The improvement over the Amsler Patent resides principally in the fact that the present invention is constructed with substantially fewer moving parts and is therefore less costly to manufacture and more easily maintained. As will be more particularly pointed out when the details of the construction of the preferred embodiment are set out herein, the present invention does not require the use of springs, pawls, and various other small parts which are subject to wear and deterioration during use.
The present invention is also a significant advance over the invention described in the Stecke Patent, supra, in that manner in which the various moving parts are fabricated such that the full force of the exploding gases reacting on the bolt are resisted by a rigid pin in such a fashion that repeated use over prolonged periods does not deleteriously effect the functioning of the firearm.
Another advantage of this invention over the two above lies in a single roller concept in cooperation with a cam configuration which provides positive locking plus slow initial extraction, or withdrawal, of the fired cartridge case. The use of a single roller of an increased radius provides greater shear strength, in that shear strength is proportional to the square of the radius.